To satisfy the recent requirement for cleaning emissions from an automobile engine, there has been provided a method of employing a three way catalytic convertor, which operates to eliminate harmful emission components in an exhaust emission from the automobile engine. However, when the three way catalytic convertor is employed, it is necessary for the air-fuel ratio of the air-fuel mixture burning in an automobile engine to be adjusted to the stoichiometric air-fuel ratio so as to enhance the catalytic action of the three way catalytic convertor. For this reason, an arrangement for providing a feedback control for controlling the air-fuel ratio has conventionally been proposed, so as to adjust the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio before the air-fuel mixture is fed into combustion chambers of an automobile engine. In the conventional arrangement, a feedback control circuit, for controlling the air-fuel ratio, is formed in such a manner that an electro-magnetic valve is disposed in a fuel passageway or in an air-bleed passageway of an engine carburetor, so that the amount of fuel or air fed into the engine is regulated by the on-off control operation performed by the valve. Also, an exhaust gas sensor, which is able to detect the concentration of a particular gas component in the exhaust gas, is disposed in the feedback control circuit of the conventional arrangement for controlling the actuation of the electro-magnetic valve, via a computer unit. The employment of the electro-magnetic valve is quite conventional for regulating the amount of fuel or air, however, the regulation by the on-off control operation of the electro-hydraulic valve usually causes a fluctuation of the flow of the fuel or air. Therefore, it is often difficult to precisely adjust the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio before the mixture is fed into combustion chambers of an engine. This difficulty can be overcome if the frequency of the on-off control operation of the electro-magnetic valve is high enough to reduce the generation of the fluctuation of the flow of the fuel or air. However, since the electro-magnetic valve always employs a movable valve element having a considerable amount of inertia, it is impossible to sufficiently increase the frequency of the on-off action of the electro-magnetic valve. Further, when the wear of the valve seat, sliding portions or mechanical contacting portions of the electro-magnetic valve, as well as the durability of spring elements employed in the valve, are taken into consideration, it is also impossible to increase the frequency of the on-off control action of the electro-magnetic valve to more than a certain limited frequency level. Thus, so long as an electro-magnetic valve is employed in the feedback control circuit for regulating the amount of the flow of air or fuel, it is difficult to precisely adjust the air-fuel ratio of an air-fuel mixture to the stoichiometric air-fuel ratio.
Therefore, an object of the present invention is to provide an arrangement for controlling an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine, whereby the difficulties encountered by the conventional arrangement for controlling an air-fuel ratio of an air-fuel mixture is well eliminated.
Another object of the present invention is to provide an arrangement for controlling an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine, in which arrangement the on-off control of the flow of air or fuel is performed at a frequency which is high enough to provide a substantially continuous flow of air or fuel, without causing any fluctuation during the controlling of the air-fuel ratio of an air-fuel mixture supplied to an automobile engine.
A further object of the present invention is to provide an arrangement for controlling an air-fuel ratio of an air-fuel mixture supplied into an internal combustion engine in which no feedback control element that may cause the wear problem is used, so as to ensure that the arrangement has a long durability.
In accordance with the present invention, the fluidic element employed in the arrangement of the present invention is not provided with any movable part therein. Therefore, deterioration of the fluidic element due to wear of the element does not take place. Consequently the employment of the fluidic element of the present invention results in the present invention being less susceptible to damage than the heretofore proposed air-fuel ratio control arrangement. Further, application of a small signal flow of fluid to the fluidic element enables the element to control the flow of air or fuel and additionally, the response speed of the fluidic element reaches a high frequency of several hundred hertz. As a result, it is possible to prevent the flow of air or fuel from fluctuating during the controlling of the air-fuel ratio of an air-fuel mixture.